Terry stared incredulously. Someone moved beside him. It was Davis. He spoke in a dry voice.

"I would think," he said detachedly, "that La Rubia could catch a boatload of fish in that water with a single haul of her nets. Certainly with two."

Terry turned his head.

"But what is it? What makes these fish gather like this?"

"An interesting question," said Davis. "We'll try to find out how it happens. Even more interesting, I'd like to know why."

He moved away along the deck. Terry went close to the side rail. A few minutes later the startling glare of one of the side searchlights smote upon the water away from the incredible scene. It moved slowly back and forth. Where the light struck, the sea seemed totally commonplace. No fish could be seen. Then the white beam swept here and there in jerky leapings. There was nothing unusual on the surface, nothing beyond the limit of brightness, where the sea turned dark.

Deirdre said at Terry's side, "We didn't really expect this! I'm going to get a sample of the water, Terry. Want to help?"

She ignored his haughty withdrawal of the afternoon, and he could not stand on his dignity in the presence of such an incredible phenomenon. She got a water bucket from the nearby rack. A wave sprung up as she tried to fill the bucket overside. It touched her hand and she cried out. Terry jerked her back by the shoulder. The bucket bumped against the Esperance's side, hanging on the line attached to the rail.

"What's the matter?"

"It stung! The water stung! Like a nettle!" Shaking a little, Deirdre rubbed her wet hand with the other. "It doesn't hurt now, but it was like a stinging nettle—or an electric shock!"

Terry hauled in the bucket and set it down. He leaned far over the rail. He plunged his hand into a lifting pinnacle of the sea. Instantly, his skin felt as if pricked by ten thousand needles. But his muscles did not contract as they would in an electric shock. The sensation was on the surface of his skin alone.

He shook his head impatiently. He put his finger in the bucket he'd lifted to the deck. There was no unusual sensation. He dipped overside again. Again acute and startling hurt, from the mere contact with the water.

Deirdre still rubbed her hand. She said in a queer, surprised voice,

"Like pins and needles. It's like—like the fish-driving paddle! But worse! Much worse!"

Terry looked again at the sea glittering with the swarms of fish in hopeless, panicked agitation, confined in a specific narrow compass by something unguessable. The searchlight continued to flick here and there. The Esperance drifted away from the edge of brightness. Terry put his hand overside once more, and once more he felt the stinging, nettle-like sensation. He got a fresh bucket of water from overside. On deck, there was no strange sensation when he dipped his hand in it.

The searchlight went out abruptly and only a faint and quickly dimming reddish glow came from it. That too died.

Davis' voice gave orders. Terry said sharply, "Wait a minute!" He began to explain about the stinging of the water. But then he said, "Deirdre, you tell him! I'm going to put a submarine ear overboard. At the least we'll get fish noises on a new scale. But I've got an idea ... don't sail into the bright circle yet."

He got out the submarine ear and the recorder he'd made ready that afternoon. He started the recorder. Then he trailed the microphone overside. The sounds would be heard live through the speaker and they would be taped at the same time. At first, a blaring, confused sound came through. Terry turned down the volume.

He heard gruntings and chirpings and rustlings. Fish made those noises—not all fish, but certain species. These shrill, squeaking noises were the protests of frightened porpoises. But under and through all other sounds, a steady, unvarying hum could be easily detected. Terry had never heard anything quite like it. Its pitch was the same as that of a sixty-cycle frequency, but its tone quality was somehow sardonic and snarling. The word that came into Terry's mind was "nasty." Yes, it was a nasty sound. One didn't like it. One would want to get away from it. In the air the same unpleasant sensation is produced by noises that make one's flesh crawl.

Terry straightened up from where the recorder played upon the wet deck. Davis and Deirdre had come to listen, in the strange darkness under the sails of the Esperance.

"I've got a sort of hunch," said Terry slowly. "Let's sail across the bright patch. I'll record the sea noises all the way. I've a feeling that that hum means something."

"It's not what you'd call an ordinary sound," said Davis.

He raised his voice. One of the crew-cuts was at the schooner's wheel. He spun it. The sails filled, and the rattling of flapping canvas died away. The Esperance gathered way and moved swiftly from the glittering circle, came about, and sailed again toward the shining area. She got closer and closer to the boundary.

The recorder continued to give out the confused and frightened noises of the sea creatures, but under and through their sounds there remained the nasty and sardonic hum. It grew louder and more unpleasant—much louder in proportion to the fish sounds. At the very boundary of the bright space it was loudest of all.

But as the yacht went on, the hum dimmed. At the very center of the circle where the glitterings were brightest, the humming sound was overwhelmed by the submarine tumult of senseless fish voices. Terry dipped his hand here. The tingling was almost tolerable, but not quite.

Davis hauled more buckets of water to the deck. In two of them he found some fish, so dense was the finny multitude. Then the yacht neared the farthest limit of the bright circle. The hum from the recording instrument grew progressively louder. Again, at the very edge of the shining water, it was loudest.

The Esperance sailed across the live boundary and into the dark sea. As the boat went on, the sound dimmed....

"Definitely loudest," said Terry absorbedly, "at the edge of the circle of fish. At the line the fish couldn't cross to escape. It is if there were an electric fence in the sea. It felt like that, too. But there isn't any fence."

Davis asked evenly, "Question: what holds them crowded?"

Terry said again, groping in his mind, "They act like fish in a closing net. I've seen something like this once, when a purse-seine was hauled. Those fish were frantic because they couldn't get away. Just like these."

"Why can't they get away?" asked Davis grimly. "We haven't seen anything holding them."

"But we heard something," pointed out Deirdre. "The hum. That may be what closes them in."

Her father made a grunting noise. "We'll see about that."

He moved away, back to the stern. In moments, the Esperance was beating upwind. Presently, she headed back toward her previous position, but outside the brightness. Terry could see dark silhouettes moving about near the yacht's wheel. Then he saw another brightness at the eastern horizon, but that was in the sky. Almost as soon as he noticed it, the moon peered over the edge of the world, and climbed slowly to full view, and then swam up among the lower-hanging stars.

Immediately, the look of the sea was different. The waves no longer seemed to race the darkness with only star glitters on their flanks. The figures at the Esperance's stern were now quite distinct in the moonlight.

"You said a very sensible thing, Deirdre," said Terry. "I thought of the fish-driving paddle and its effects, but I was ashamed to mention it. I thought it would sound foolish. But when you said it, it didn't."

"I have a talent," said Deirdre, "for making foolish things sound sensible. Or perhaps the reverse. I'm going to say a sensible thing now. We haven't had dinner. I'm going to fix something to eat."

"You won't get anybody to go belowdecks right now!" said Terry.

"I thought of that," she told him. "Sandwiches."

She went below. Terry continued to watch, while figures at the stern of the schooner went through an involved process of visual measurement. It was not simple to determine the dimensions of a patch of shimmering light flashes from a boat in motion. But presently, Davis came toward him.

"It's thirteen hundred yards across," he told Terry. "Plus or minus twenty."

"I didn't expect all this," Davis said, frowning. "I've been making guesses and hoping fervently that I was wrong. And I have been, but each time the proof that I was wrong has led to new guesses, and I'm afraid to think those guesses may be right."

"I can't begin to guess yet," said Terry.

"You will!" Davis assured him. "You will! You try to add up things.... A half-mile-wide patch of foam that piles up thirty feet above the sea...."

"And into which," Terry interrupted, "a sailing ship does not sink but drops out of sight as if there were a hole in the sea."

Davis turned sharply toward him.

"There were some photographs and a newspaper clipping on the cabin table," explained Terry. "I suspected they might have been put there for me to see."

"Deirdre, perhaps," said Davis. "She's resolved to involve you in this. You've got scruples, so she suspects you of having brains. Yes. You'll add those things up. You'll include the remarkable success of a fishing boat named La Rubia and the fact that she sometimes brings in very strange fish ... And then you'll add ..."

His eyes flickered aloft. A shooting star streaked across one-third of the sky leaving a trail of light behind it. Then it went out.

"You'll even be tempted," said Davis, "to include something like that in your guesses! And then you'll try to come up with a total for the lot. Then you'll be as troubled as I am."

He paused a moment.

"You said you wanted to be put ashore as soon as the gadget you made today was tested. I hope you've changed your mind, or will. That tape-recording may mean something to somebody. We wouldn't have heard that very singular noise but for you."

"I withdraw the business of going ashore," said Terry uncomfortably. "I'm going to ask another question. What are those little spheres that I saw in the photographs on the cabin table? Were they found fastened to the fish?"

"So I'm told," said Davis. "They are made of plastic. One was on a fish caught by a chief petty officer of the United States Navy. Four have been found on fish brought into the market by La Rubia. They could conceivably be a joke, but it's very elaborate! Somebody tried to cut one open and it burst to hell-and-gone. Terrific pressure inside. The metal parts inside were iridium. The others haven't been cut open. They're—" Davis' tone was dry. "They're being studied."

A figure came out of the forecastle and walked aft. It was Nick. He stopped to say, "I called Manila and got a loran fix on us. We're right at the place La Rubia heads for every time she sneaks away from the rest of the fishing fleet. It seems that she hauls her nets yonder."

He nodded toward the circular area of luminosity on the sea. "It looks smaller than when I went below deck."

Davis stared. He seemed to stiffen.

"It does. We'll make sure."

He went aft. Deirdre came up with sandwiches. Terry took the tray from her and followed her toward the others.

"Cigars, cigarettes, candy, sandwiches?" she asked cheerfully.

Davis was back at the task of measuring the angle subtended by the patch of shining sea, and then closely estimating its distance from the Esperance. He said, "It is smaller. Eleven hundred yards, now."

"When La Rubia was here today," said Terry, "it might have been a couple of miles across. Even that would be a terrific concentration of fish! They're not all at the surface."

Davis said with impatience, seemingly directed against himself, "It's narrowed two hundred yards in the past half-hour. It must be tending toward something! There has to be a conclusion to it! Something must be about to happen!"

Deirdre said slowly, "If it's the equivalent of a seine being hauled, with a hum instead of a net, what's going to happen when it's time for the fish to be boated?"

Davis ignored her for a moment. Then he said irritably, "Everyone seems to have more brains than I do! Tony, break out those gun-cameras. Nick, get back and report if the bright spot's getting any smaller. I wish you weren't here, Deirdre!"

The two crew-cuts moved to obey. Terry, alone, had no specific duty assigned to him on the yacht, unless tending to the recorder was it. He bent over the instrument which was playing in the air anything that a trailing microphone picked up under water. He raised the volume a trifle. He could still hear the singular noises of the agitated fish mixed in with the thin, strangely offensive humming sound. He heard small thumpings, and realized that they were the footfalls of his companions on the deck of the Esperance, transmitted to the water. He heard ...

Tony came abovedecks with an armful of mysterious-looking objects which could not be seen quite clearly in the slanting moonlight. He put two of them down by the wheel and passed out the others. He silently left one for Terry and another for Deirdre, while Terry adjusted tone and volume on the recorder for maximum clarity.

"What are those?" asked Terry.

"Cameras," said Deirdre. "Mounted on rifle stocks, with flashbulbs in the reflectors. You aim, pull the trigger, and the shutter opens as the flashbulb goes off. So you get a picture of whatever you aim at, night or day."

"Why ..."

"There was a time when my father thought they might be useful," said Deirdre. "Then it looked like they wouldn't. Now it looks like they may."

Terry was tempted to say, "Useful for what?" But Davis' vague talk of unpleasant wrong guesses which led to even less pleasant ones had already been an admission that no convincing answer could be given him. Davis came over to him.

"This has me worried," he said in a frustrated tone of indecision. "We must be near the end of some process that I didn't suspect, and the conclusion of which I can't guess. I don't know what it is, and I don't know what it's for. I only know what it's tied in with."

Terry said absorbedly, "Two or three times I've picked up some new kinds of sounds. You might call them mooing noises. They're very faint, as if they were far away, and there are long intervals between them. I don't think they come from the surface."

Davis made an irresolute gesture. He seemed to hesitate over something he was inclined to accept. Deirdre protested before he could speak. "I don't think what you're thinking is right!" she said firmly. "Not a bit of it! Whatever happens will be connected with the fish. La Rubia has been around this sort of thing over and over again! We haven't been running the engine and we haven't been making any specific noises in the water to arouse curiosity! If anything were going to happen to us, it would have happened to La Rubia before now! It would be ridiculous to run away just because I'm on board!"

Terry, bent intently over the recorder, suddenly felt a cold chill run up and down his spine. His mind told him it was ridiculous to associate distant mooing sounds, underwater, with a completely unprecedented, frantic gathering of fish into one small area, and come up with the thought that something monstrous and plaintive was coming blindly to feed upon fellow creatures of the sea. There was nothing to justify the thought. It was out of all reason. But his spine crawled, just the same.

"The circle's only eight hundred yards across, now," said Davis, uneasily. "The fish can't crowd together any closer! But Doug went overboard with diving goggles, and he says there's a column of brightness as far down as he can make out."

Terry looked up.

"He went overboard? Didn't he tingle?"

"He said it was like baby nettles all over," Davis protested, as if it were someone's fault. "But he didn't sting after he came out. It must be ..."

A mooing sound came out of the recorder. It was fainter than the other sounds and very far away. It must have been of terrific volume where it originated. It lasted for many seconds, then stopped.

"I should have been recording," said Terry. "That sound comes up about every five minutes. I'll catch it next time."

Davis went away, as if he wanted to miss the noise and the decision it would force upon him. Yet Terry told himself obstinately that there was no reason to connect the mooing sound with the crazed fish herd half a mile away. But somehow he couldn't help thinking there might be a connection.

The ship's clock sounded seven bells. Deirdre said, "The brightness is really smaller now!" The patch of flashes was no more than half its original size. Terry pressed the recording button and straightened up to look more closely. Right then Deirdre said sharply, "Listen!"

Something new and quite unlike the mooing noise now came out of the recorder.

"Get your father," commanded Terry. "Something's coming from somewhere!"

Deirdre ran across the heaving deck. Terry shifted position so he could manipulate the microphone hanging over the yacht's side into the water. Davis arrived. His voice was suddenly strained and grim. "Something's coming?" he demanded. "Can you hear any engine noise?"

"Listen to it," said Terry. "I'm trying to get its bearing."

He turned the wire by which the submarine ear hung from the rail. The chirpings and squealings and squeakings changed volume as the microphone turned. But the new sound, of something rushing at high speed through the water—that did not change. Terry rotated the mike through a full circle. The fish noises dwindled to almost nothing, and then increased again. The volume of the steady hum changed with them. But the rushing sound remained steady. Rather, it grew in loudness, as if approaching. But the directional microphone didn't register any difference, whether it received sound from the north, east, south, or west.

It was a booming sound. It was a rushing sound. It was the sound of an object moving at terrific speed through the water. There was no engine noise, but something thrust furiously through the sea, and the sound grew louder and louder.

"It's not coming from any compass course," said Terry shortly. "How deep is the water here?"

"We're just over the edge of the Luzon Deep," said Davis. "Four thousand fathoms. Five. Maybe six."

"Then it can only be coming from one direction," said Terry. "It's coming from below. And it's coming up."

For three heartbeats Davis stood perfectly still. Then he said, with extreme grimness, "Since you mention it, that would be where it's coming from."

He turned away and shouted a few orders. The crewmen scurried swiftly. The yacht's head fell away from the wind. Terry listened again to the rushing sound. There seemed to be regular throbbings in it, but still no engine noise. It was a steady drone.

"Bazooka shells ought to discourage anything," Davis said in an icy voice. "If it attacks, let go at it. But try to use the gun-cameras first."

The Esperance rolled and wallowed. Her bows lifted and fell. Her sails were black against the starry sky overhead. Two of the crew-cuts settled themselves at the starboard rail. They had long tubes in their hands, tubes whose details could not be seen. The wind hummed and thuttered in the rigging. Reef-points pattered. Near the port rail the recorder poured out the amplified sounds its microphone picked up from the sea. The sound of the coming thing became louder than all the other noises combined. It was literally a booming noise. The water started to bubble furiously as it parted to let something rise to the surface from unthinkable depths.

Doug put two magazine-rifles beside Terry and Deirdre, then he moved away. Deirdre had a clumsy object in her hands. It had a rifle-stock and a trigger. What should have been the barrel was huge—six inches or more in diameter—but very short. That was the flashbulb reflector. The actual camera was small and on top, like a sight.

"We'll aim these at anything we see," said Deirdre composedly, "and pull the trigger. Then we'll pick up the real rifles and see if we must shoot. Is that all right?"

She faced the shining patch of ocean. Davis and the crew-cut at the wheel faced that way. Tony and Jug stood with the clumsy tubes of bazookas facing the same direction. Doug had taken a post forward, with a camera-gun and a magazine rifle. He had the camera in hand, to use first.

It seemed that hours passed, but it must have been just a few minutes. Nothing out of the ordinary seemed to be taking place anywhere. The moon now shone down from a sky in which a few thin wisps of cloud glowed among the stars. Sharp-peaked waves came from one horizon and sped busily toward the other. The yacht pitched and rolled, its company strangely armed and expectant. The recorder gave out a droning, booming, rushing sound which grew louder with ever-increasing rapidity. Now the sound reached a climax.

From the very center of the glinting circle of sea, there was a monstrous splashing sound. A phosphorescent column rose furiously from the waves. It leaped. Water fell back and ... something soared into the air. Sharp, stabbing flashes of almost intolerably white light flared up. The gun-cameras fired their flashbulbs without a sound.

It was then that Terry saw it—in mid-air. He swung the gun-camera, and a flash from another gun showed him that he would miss. He jerked the gun to bear and pulled the trigger. The flash illuminated it vividly. Then night again.

It was torpedo-shaped and excessively slender but very long. It could have been a living thing, frozen by the instantaneous flash. It could have been something made of metal. It leaped a full fifty feet clear of the waves and then tumbled back into the ocean with a colossal splash. Then there was silence, except for the sounds of the sea. Terry had the magazine-rifle still in his hands. Tony and Jug waited with their bazookas ready. It occurred to Terry that yachts are not customarily armed with bazookas.

"That—wasn't a whale," said Deirdre unsteadily.

The recorder bellowed suddenly. It was the hum that had been heard before: the nasty, sixty-cycle hum that surrounded the captive fish. But it was ten, twenty, fifty times as loud as before.

The fish in the bright-sea area went mad. The entire surface whipped itself to spray, as fish leaped frenziedly to get out of the water, which stung and burned where it touched.

Then, very strangely, the splashing stopped. The brightness of the sea decreased. A while later the enormous snarling sound was noticeably less loud than it had been at that first horrible moment.

The wind blew. The waves raced. The Esperance's bow lifted and dipped. The noise from the loudspeaker system—the noise from the sea—decreased even more. One could hear the squeakings and chitterings of fish again. But they were very much fainter. Presently the humming was no louder than before the strange apparition. By that time the fish-sound had died away altogether. The nearer normal noises remained. The hum was receding. Downward.

Davis came to Terry, where he stood by the recording instrument.

"The fish have gone," he said in a flat voice, "they've gone away. They didn't scatter. We'd have seen it. Do you realize where they went?"

Terry nodded.

"Straight down. Do you want to hear an impossible explanation?"

"I've thought of several," said Davis.

Doug came and picked up the gun-cameras that Terry and Deirdre had used and went away with them.

"There's a kind of sound," said Terry, "that fish don't like. They won't go where it is. They try to get away from it."

Deirdre said quietly, "I would too, if I were swimming."

"Sound," said Terry, "in water as in air, can be reflected and directed, just as light can be. A megaphone turns out one's voice in a cone of noise, like a reflector on a light. It should be possible to project it. One can project a hollow cone of light. Why not a hollow cone of sound, in water?"

Davis said with an unconvincingly ironic and skeptical air, "Indeed, why not?"

"If such a thing were done," said Terry, "then when the cone of sound was turned on, the fish inside it would be captured as if by a conical net. They couldn't swim through the walls of sound. And then one can imagine the cone made smaller; the walls drawn closer together. The fish would be crowded together in what was increasingly like a vertical, conical net, but with walls of unbearable noise instead of cord. It would be as if the sea were electrified and the fish were shocked when they tried to pass a given spot."

"Preposterous, of course," said Davis. But his tone was not at all unbelieving.

"Then suppose something were sent up to the top of the cone, and it projected some kind of a cover of sound on the top of the cone and imprisoned the fish with a lid of sound they couldn't endure. And then suppose that thing sank into the water again. The fish couldn't swim through the walls of noise around them. They couldn't swim through the lid of sound above them. They'd have to swim downward, just as if a hood were closing on them from above."

"Very neat," said Davis. "But of course you don't believe anything of the sort."

"I can't imagine what would produce that sound in that way and send up a cork of sound to take the fish below. And I can't imagine why it would be done. So I can't say I believe it."

Davis said slowly, "I think we begin to understand each other. We'll stay as close to this place as we can until dawn, when we will find nothing to show that anything out of the ordinary happened here."

"Still less," said Terry, "to hint at its meaning. I've been doing sums in my head. That bright water was almost solid with fish. I'd say there was at least a pound of fish to every cubic foot of sea."

"An underestimate," said Davis judicially.

"When the bright patch was a thousand yards across—and it was even more—there'd have been four hundred tons of fish in the top three-foot layer."

Davis seemed to start. But it was true. Terry added, "The water was clear. We could see that the packing went on down a long way. Say fifty yards at least."

"Y-yes," agreed Davis. "All of that."

"So in the top fifty yards, at one time, there were at least twenty thousand tons of fish gathered together. Probably very much more. What La Rubia carried away couldn't be noticed. All those thousands of tons of fish were pushed straight down. Tell me," said Terry, "what would be the point in all those fish being dragged to the bottom? I can't ask who or what did it, or even why. I'm asking, what results from it?"

Davis grunted.

"My mind stalls on who or what and why. And I'd rather not mention my guesses. I.... No!"

He moved abruptly away.

The Esperance remained under sail near the patch of sea that had glittered earlier and now looked exactly like any other square mile of ocean. The recorder verified the position by giving out, faintly, the same unpleasant humming noise, either louder or fainter. A soft warm wind blew across the waters. The land was somewhere below the horizon. The reel of recorder-tape ran out. It was notable that there were very few fish sounds to be heard, now. Very few. But the hum continued.

Toward morning it stopped abruptly. Then there was nothing out of the ordinary to be observed anywhere.

The sun rose in magnificent colorings. The sky was clear of clouds. Again the waves looked like living, leaping, joyous things. Gulls were squawking.

Doug came up from belowdecks. He carried some photographic prints in his hand. He'd developed and printed what the gun-cameras had photographed when the mysterious object, or beast, leaped clear of the sea. There were seven different pictures. Four showed flashbulb-lighted sections of empty ocean. One showed a column of sea water rising at fantastic height from the sea. Another one showed the edge of something at the very edge of the film.

The seventh picture Terry recognized. It was what he'd seen when the flashbulb of his gun-camera went off. The focus was not sharp. But it was neither a whale nor a blackfish—not even a small one—nor was it a shark. It was not a squid. It was not even a giant manta. The picture was a blurry representation of something unreal made for an unimaginable purpose, under abnormal conditions.

Deirdre looked at it over his shoulder. It could be a living creature. It could be ... anything.

"You said you didn't like mysteries," commented Deirdre. "Are you sorry you came?"